Substrate alignment method and apparatus

ABSTRACT

A substrate  110  that is not lying flat on its substrate tray  100  can present significant process problems when a vacuum pickup attempts to pick up the substrate and fails due to the lack of a proper bond forming between the pickup and the substrate  110 . The substrate  110  left behind on the substrate tray  100  could require human intervention. Intervention slows down the manufacturing process and increases costs. A method and apparatus to ensure that substrates are laying flat when presented to the vacuum pickup pad  220  is disclosed. A plate  320  with protrusions 320 is raised into a substrate tray  100  with holes. The protrusions 320 lift the substrates  110  up off the bottom of the substrate tray  100  and ensure that they are laying flat when presented to the vacuum pickup pad  220.

FIELD OF THE INVENTION

[0001] This invention relates generally to semiconductor substrates, andparticularly to reducing errors and mistakes during the packagingprocess of semiconductor substrates.

BACKGROUND OF THE INVENTION

[0002] Semiconductor devices are fabricated on wafers usually made outof silicon. The wafers are then cut into individual substrates, tested,and then packaged. There are many different ways of packaging asubstrate, including Ball Grid Arrays (BGA), Flip Chip, Multi-chipModules, Chip-on-a-Board, etc. Many of these packaging techniquesinvolve grasping the substrate with a vacuum pickup from one location,manipulating the substrate in some way, and then placing it back downonto another or the same location. For example, when using flip chippackaging, the substrate must be lifted from a tray containing thesubstrates, flipped, and then solder balls are mounted onto pads locatedon the substrates.

[0003] In order for the vacuum pickup to obtain a good temporary bondwith the substrate, the substrate should be horizontal with respect tothe vacuum pickup. In some cases, when the substrates are lying on asubstrate tray, the substrates are not lying perfectly horizontalbecause they may not be fully seated within depressions built into thetray designed to hold the substrates. When the substrate is not fullyhorizontal with respect to the vacuum pickup the chances of the vacuumpickup being able pick up the substrate goes down. Should a substratenot be picked up, intervention is often required to fix the positioningof the substrate to permit the vacuum pickup to attach to the substrate.

[0004] Intervention is not desired in an efficient packaging processsince it often requires stopping the packaging process and a humanoperator making the required adjustments. Intervention slows down theprocess and increases overall production costs.

[0005] Solutions using custom designed substrate trays can reduce thenumber of substrates that are not lying horizontally, but they typicallyrequire a special tray for each size and type of substrate. Thisincreases the costs and overhead associated with the packaging process,especially in packaging plants that process a wide variety of differentsubstrates.

[0006] Therefore, a need has arisen for a method and apparatus that canincrease the probability of a vacuum pickup forming a solid bond with asubstrate by ensuring that the substrates are lying horizontal withrespect to the vacuum pickup.

SUMMARY OF THE INVENTION

[0007] In one aspect, the present invention provides a method ofensuring proper contact between a plurality of substrates and a liftingdevice with a plurality of nozzles in a semiconductor packaging processwherein the substrates are placed one each in depressions in a substratetray and in each depression there is a hole, the method comprising:raising a plate with a plurality of protrusions through the tray, witheach protrusion going through a hole, lowering the lifting device ontothe tray, stopping when nozzles from the lifting device comes intocontact with the substrates, and applying a vacuum at the nozzles totemporarily attach the substrates to the nozzles.

[0008] In another aspect, the present invention provides an apparatusfor lifting substrates in a semiconductor packaging process, theapparatus comprising: a plate with a plurality of protrusions, asubstrate tray with a plurality of depressions and a hole in eachdepression coupled to the plate, the substrate tray capable of holding asubstrate in each depression, a lifting device with a plurality ofnozzles coupled to the substrate tray, the lifting device capable ofattaching to the substrates and lifting them out of the substrate tray,a first actuator coupled to the plate, the first actuator to raise andlower the plate; and a second actuator coupled to the lifting device,the second actuator to lower and raise the lifting device.

[0009] The present invention provides a number of advantages. Forexample, use of a preferred embodiment of the present invention reducesthe probability of requiring intervention in a packaging process byreducing the chance of a substrate not being picked up by a vacuumpickup down to almost zero. The net result is an increase inproductivity.

[0010] Also, use of a preferred embodiment of the present inventionincurs no additional cost during normal packing operations. The onlycosts incurred involve the creation of a plate used to lift thesubstrates.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above features of the present invention will be more clearlyunderstood from consideration of the following descriptions inconnection with accompanying drawings in which:

[0012]FIGS. 1a and 1 b provide a top-down and side view of a substratetray designed to hold substrates;

[0013]FIGS. 2a-c provide views of a vacuum pickup attempting to pick upsubstrates where some of the substrates are not lying flat in thesubstrate tray;

[0014]FIGS. 3a-d provide views of a vacuum pickup picking up substrateswith use of an apparatus for ensuring that the substrates are flat whenpresented to the pickup according to a preferred embodiment of thepresent invention;

[0015]FIG. 4 provides a plan view of an apparatus for ensuring thatsubstrates are flat when presented to the pickup according to apreferred embodiment of the present invention;

[0016]FIG. 5 provides an apparatus for ensuring that substrates are flatwhen presented to the pickup according to a preferred embodiment of thepresent invention;

[0017]FIGS. 6a and 6 b provide other apparatus for ensuring thatsubstrates are flat when presented to the pickup according to apreferred embodiment of the present invention; and

[0018]FIG. 7 provides a view of a portion of a flip chip packagingprocess using an apparatus for ensuring that substrates are flat whenpresented to the pickup according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0019] The making and use of the various embodiments are discussed belowin detail. However, it should be appreciated that the present inventionprovides many applicable inventive concepts, which can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the invention,and do not limit the scope of the invention.

[0020] Referring now to FIG. 1a, a diagram provides a top-down view of asubstrate tray 100. The substrate tray 100, in some packagingapplications, the substrate tray is referred to as a Jedec tray, is usedto hold a number of singulated units 110 (substrates that have been cutfrom a silicon wafer). Alternatively, the singulated units 110 may becomplete integrated circuit units wherein the unit comprising aplurality of dies that were cut from silicon wafers and the unit isready for functional and error testing once electrical connectivity ismade. The tray 100 holds the singulated units 110 in a neat and orderlyfashion to facilitate easy and accurate handling. To facilitate preciseplacement of the singulated units 110, the tray 100 may feature properlysized indentations, ridges, or bumps (not shown) for use in aligning thesingulated units 110.

[0021] Referring now to FIG. 1b, a diagram provides a view along onelateral axis of the substrate tray 100 displayed in FIG. 1a. Forillustrative purposes, the tray 100 is shown as if it is clear,permitting a view of the singulated units 110 lying within the tray.FIG. 1b illustrates an idealized situation where the singulated units110 lying in the tray 100 are lying flat, perhaps within theindentations, ridges, or bumps (not shown) present on the tray 100, aswell as being equally spaced with respect to one another.

[0022] For packaging operations where precision is a necessity, theposition of the singulated units 110 within the tray 100 is crucial. Dueto the indentations, ridges, or bumps used for aligning the singulatedunits 110 within the tray 100, occasionally, some singulated units 110are placed in the tray in such a way that they do not seated properlywithin the indentations, ridges, or bumps. When this occurs, thesingulated units 110 can lie at an angle with respect to the tray 100.

[0023] Since the packaging process is typically entirely machine driven,both for increased speed and accuracy purposes, a misaligned singulatedunit may result in a packaged product that does not work properly orworse, it may cause the packaging process to be halted to allow humanintervention to fix the alignment problem. Therefore, it is desirable tominimize the occurrence of misaligned singulated units.

[0024] After the singulated units are in place in the trays, a liftingunit is used to pick up the singulated units from the tray and move themto position for a packaging operation to take place. The lifting unit issometimes referred to as a back-up unit and uses vacuum to lift up thesingulated units from the tray. In a flip chip packaging process, anexample of the use of the back-up unit is when the singulated units arelifted from the trays by the back-up unit, flipped so that a side thatwas formerly resting on the bottom of the tray is now facing upwards,and solder bumps are applied to pads on the substrate.

[0025] Referring now to FIGS. 2a-c, diagrams illustrate the lifting ofsingulated units 110 from a tray 100 using a lifter unit 210. FIG. 2aillustrates the lifter unit 210 moving in a downward motion towards thetray 100 and the singulated units 110 therein. FIG. 2b illustrates thelifter unit 210 nearing a bottom limit of its travel, resting almostimmediately upon the singulated units 110. When the lifter unit 210 isat the bottom of its travel, a vacuum is applied and the singulatedunits 110 are attached to individual vacuum pads 220 of the lifter unit210.

[0026] With the vacuum applied and the singulated units 110 are attachedto the individual vacuum pads 220 of the lifter unit 210, the lifterunit 210 begins to travel in an upward motion to lift the singulatedunits 110 out of the tray 100. In some packaging operations, the lifterunit 210 also incorporates other functionality, such as flipping thesingulated units 110 as well. Unfortunately, some of the singulatedunits 110, the ones that were not laying flat on the tray 100, were notlifted by the lifter unit 210. This may have been due to an impropervacuum pressure being made with the individual vacuum pads 220 that area direct result of the singulated units 110 not lying flat on the tray100.

[0027] A result of some of the singulated units not being picked up bythe lifter unit 210 may be the singulated units being rerun through thepackaging process, the packing process may be stopped to permit humanintervention in fixing the positioning of the singulated units, or thesingulated units may be packaged incorrectly and the discarding of thesingulated unit and any packaging materials already used on thesingulated units.

[0028] An apparatus that can reduce or eliminate the problem of thesingulated units not laying flat in the trays can increase theefficiency of the packaging process and possibly reduce the number offaultily packaged units. Such an apparatus can increase profits for themanufacturer and reduce waste.

[0029] Referring now to FIGS. 3a-d, diagrams illustrate an apparatus foreliminating the problem of singulated units not resting flat on the trayaccording to a preferred embodiment of the present invention. Ratherthan attempting to pick up the singulated units 110 from the tray 300with the lifter unit 210 while the singulated units 110 are lyingdirectly upon the tray 300, in a preferred embodiment of the presentinvention, a back-up plate 310 with a plurality of protrusions 320protruding from one surface of the back-up plate 310 moves in an upwarddirection from beneath the tray 300. The back-up plate 310 is driven bya pneumatic actuator (not shown) that moves the plate in an up and downmotion. According to another preferred embodiment of the presentinvention, the back-up plate 310 may be driven by a hydraulic actuatorrather than a pneumatic actuator. Accordingly, the tray 300 necessarilyhas a series of holes in its bottom to mate with the protrusions 320from the back-up plate 310. The holes should be sufficiently small sothat the singulated units 110 do not fall through. The back-up plate 310is preferably fabricated from a metallic material, such as aluminum orsteel, to provide thermal stability and good strength. However, othermaterials which are capable of withstanding a high temperature processesand possibly exposure to caustic chemicals, such as carbon fiber, areusable.

[0030] The protrusions 320 fit through openings at the bottom of thetray 300 and make contact with the singulated units 110 (FIG. 3b). Asthe tray 310 continues to move up, the protrusions 320 lift thesingulated units 110 up off the bottom of the tray 300. According to apreferred embodiment of the present invention, the protrusions 320 areof sufficient height to raise the singulated units 110 above the bottomof the tray 300 plus a sufficient amount to provide clearance for anyindentations, bumps, or ridges that may be present on the tray 300.Additionally, the tops of the protrusions 320 (the part that makescontact with the singulated units 110) should be flat to provide astable resting surface for the singulated units 110.

[0031] By raising the singulated units 110 up off the bottom of the tray300, the back-up plate 310 ensures that the singulated units 110 in thetray are laying flat. This creates a good contact point for individualvacuum pads 220 of the lifter unit 210 when they are moved down byanother actuator (not shown) to pick up the singulated units 110 (FIG.3c). With each singulated unit making good contact with the vacuum pads220 of the lifter unit 210, all are lifted out of the tray when thelifter unit 210 moves back out of the tray 300 (FIG. 3d).

[0032] According to a preferred embodiment of the present invention, theactuators used to raise the plate and to lower the lifting device aredriven by compressed air (pneumatic). Alternatively, the actuators maybe hydraulic in nature or they may be electrical motors with finecontrol.

[0033] Referring now to FIG. 4, a diagram provides a plan view of thetray 100 and the back-up plate 310 with the protrusions according to apreferred embodiment of the present invention. The plan view illustratesthe tray 300 with the holes in its bottom to match the protrusions 320from the back-up plate 310. Once again, any depressions, ridges, orbumps present at the bottom of the tray 300 are not displayed.

[0034]FIG. 4 displays the protrusions 320 being square or rectangular incross section. According to another preferred embodiment of the presentinvention, the cross section of the protrusions can be of othergeometric shapes such as circles, ovals, triangle, for example. It ispreferred that the cross section be of a shape that is easy tomanufacture and provides some built-in measure of ruggedness. Forexample, while a protrusion with a multi-faceted cross section wouldsurely function, the multiple facets would be difficult to manufactureand the facets themselves would likely be easily damaged during use.

[0035] Referring now to FIG. 5, a diagram provides a plan view of a tray510 with protrusions 520 with a circular cross section according to apreferred embodiment of the present invention. As discussed previously,the circular cross section of the protrusions is relatively easy tomanufacture and at the same time, provides a measure of ruggedness forincreased durability during use.

[0036] To maximize flexibility in the design of the plates used forlifting the substrates, it can be preferred that the back-up plates bedesigned in a modular fashion so that several of them may be joinedtogether to form a larger plate to meet changing needs and requirements.

[0037] Referring now to FIGS. 6a and 6 b, diagrams illustrate the use ofa basic plate building block to create custom plate sizes according to apreferred embodiment of the present invention. A basic plate can becreated, for example, in FIG. 6a the basic block is a linear plate 620with eight protrusions, which can then be connected together to create alarger plate 610. The use of a basic plate allows the flexibility tosupport substrate trays of almost any arbitrary size

[0038] An example of the use of a preferred embodiment of the presentinvention is in a flip chip packaging process. One step in the packagingof substrates using flip chip packages is the application of solderbumps to ball lands dispersed through out a substrate. In order to applythe solder bumps to the substrates, it is necessary that the substratesbe flipped. Using the previously described, prior art method forflipping substrates, a significant percentage of the substrates are notflipped due to the substrates not lying flat in the Jedec trays andsubsequently not being picked up by the lifting device. Use of thepresent invention would reduce the number of unflipped substrates andmachine errors.

[0039] Referring now to FIG. 7, a diagram illustrates a portion of theflip chip packaging process 700 utilizing the lifting plates accordingto a preferred embodiment of the present invention. The substrates areloaded into a substrate tray at a loading station 710 and are movedalong the packaging process 700. When the substrate tray arrives at aflipping station 715, a plate with appropriately sized protrusions islifted into the bottom of the substrate tray, lifting the substratesfrom the bottom of the tray. As discussed previously, in certainapplications, a substrate lifting operation can be combined with anothermechanical operation. In the case of flip chip packaging, the substratelifting operation is commonly combined with a flipping operation. Aflipping arm with vacuum pads moves in a downward direction towards thelifted substrates and a vacuum pressure is applied at the vacuum pads tocreate a temporary bond between the substrates and the vacuum pads. Theflipping arm lifts and flips the singulated units in a single rotarymotion.

[0040] Once flipped, the substrates are moved to a solder ballapplication station 720 where the solder bumps are attached to thesubstrates. The substrates with attached solder bumps continue down theflip chip packaging process 700 where they receive additional processsteps.

[0041] While this invention has been described with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Various modifications and combinations ofthe illustrative embodiments, as well as other embodiments of theinvention, will be apparent to persons skilled in the art upon referenceto the description. It is therefore intended that the appended claimsencompass any such modifications or embodiments.

What is claimed is:
 1. A method of ensuring proper contact between aplurality of substrates and a lifting device with a plurality of vacuumpads in a semiconductor packaging process wherein the substrates areplaced one each in depressions in a substrate tray and in eachdepression there is a hole, the method comprising: raising a plate witha plurality of protrusions through the tray, with each protrusion goingthrough a hole; lowering the lifting device onto the tray; stopping whenthe vacuum pads from the lifting device comes into contact with thesubstrates; and applying a vacuum at the nozzles to temporarily attachthe substrates to the nozzles.
 2. The method of claim 1, wherein theprotrusions on the plate are of sufficient height to lift the substratesup off the bottom of the tray.
 3. The method of claim 1, wherein theprotrusions on the plate are of sufficient height to lift the substratesup off the bottom of the tray and over the depressions in which theylay.
 4. The method of claim 1, wherein the holes in the tray aresufficiently size to permit the protrusions to come through the bottomof the tray.
 5. The method of claim 4, wherein the holes in the tray aresmall enough to prevent the substrates from falling through.
 6. Themethod of claim 1, wherein the method further comprising the step ofraising the lifting device out of the tray after applying the vacuum. 7.The method of claim 1, wherein the protrusions are arranged in atwo-dimensional array on the plate.
 8. The method of claim 1, whereinthe protrusions are arranged in a linear array on a strip and aplurality of strips are joined to form the plate.
 9. An apparatus forlifting substrates in a semiconductor packaging process, the apparatuscomprising: a plate with a plurality of protrusions; a substrate traywith a plurality of depressions and a hole in each depression coupled tothe plate, the substrate tray to hold a substrate in each depression; alifting device with a plurality of vacuum pads coupled to the substratetray, the lifting device to attach to the substrates and lift thesubstrates out of the substrate tray; a first actuator coupled to theplate, the first actuator to raise and lower the plate; and a secondactuator coupled to the flipping device, the second actuator to lowerand raise the lifting device.
 10. The apparatus of claim 9, wherein theprotrusions are flat at their tops.
 11. The apparatus of claim 10,wherein the protrusions are rectangular in cross section.
 12. Theapparatus of claim 10, wherein the protrusions are square in crosssection.
 13. The apparatus of claim 9, wherein the first and secondactuators are pneumatic actuators.
 14. The apparatus of claim 9, whereinthe first and second actuators are hydraulic actuators.
 15. Theapparatus of claim 9, wherein the protrusions are of sufficient heightso that when the plate is raised into the bottom of the tray, theprotrusions lift the substrates up off the bottom of the tray.
 16. Theapparatus of claim 9 further comprising a third actuator coupled to thelifting device, the third actuator to move the lifting device away fromthe tray to a different position.
 17. The apparatus of claim 16, whereinthe third actuator moves the lifting device after the lifting device hasbeen raised back up after lifting substrates from the substrate tray.18. The apparatus of claim 9 further comprising a vacuum generatorcoupled to the flipping device, the vacuum generator to produce a vacuumat each vacuum pad of the flipping device to form a temporary bondbetween the vacuum pad and the substrate.
 19. A system for applyingsolder bumps to substrates in a flip chip packaging process, the systemcomprising: a loader station to load substrates into a substrate tray; aflipping station coupled to the loader station, the flipping station toflip substrates held in the substrate tray, the flipping stationcomprising: a plate with a plurality of protrusions; a flipping devicewith a plurality of vacuum pads coupled to the substrate tray, theflipping device to attach to the substrates, lift the substrates out ofthe substrate tray, and flip the substrates; a first actuator coupled tothe plate, the first actuator to raise and lower the plate; a secondactuator coupled to the flipping device, the second actuator to lowerand raise the flipping device; a solder bump application station coupledto the flipping station, the solder bump application station to applyand bond solder bumps to the substrates; and wherein the first actuatorraises the plate into the bottom of the substrate tray, the secondactuator lowers the flipping device into the substrate tray when thesubstrate tray is in the flipping station.
 20. The system of claim 19further comprising a vacuum generator coupled to the flipping device,the vacuum generator to produce a vacuum at each vacuum pad of theflipping device to form a temporary bond between the vacuum pad andsubstrates.
 21. The system of claim 20, wherein the flipped substratesare placed back into the substrate tray after being flipped by theflipping station.